In case of a conventional radial metallic foam filter, if the exhaust gas is flown in towards the inner pipe, a high pressure is exerted on the blocked rear end portion of the inner pipe to increase the flow rate at the rear end portion, and a low pressure is exerted on the front end portion of the inner pipe to decrease the flow rate at the front end portion. In this way, where the flow rate becomes different throughout the filter, a large amount of particulate matters are collected at the rear end portion of high flow rate and a less amount of particulate matters are collected in the front end portion for the same period of time because of the lower flow rate. In this case, if a reproduction occurs, the filter can be damaged or distorted due to the temperature gradient. In addition, it causes an increase in the back pressure before the reproduction occurs to adversely affect the performance of the filter.
Conventionally, the sealing material for fume reduction devices has employed a ceramic seal. The ceramic seal is inherently easily deformed and provides excellent machining characteristics. However, when the ceramic seal is used in a fume reduction device, repeated heating and cooling, and the thermal impact degrade the durability thereof.
Further, a high-temperature exhaust gas flows into a fume reduction device and is discharged to the outside via a filter. During this course of action, the high-temperature of the exhaust gas is transferred to each part of the fume reduction device. In addition, the conventional sealing mat is destroyed or burned out due to the periodic heating and cooling and the thermal shock.
In addition, the porous tube is limited to the convenience in the manufacturing of a metallic foam and functions to maintain the shape thereof. Thus, the flow rate of the exhaust gas cannot be reduced and the stagnant time inside the filter cannot be increased. In addition, the probability of contacting particulate matters with the metallic foam filter cannot be increased so that the efficiency of collection cannot be improved.
Further, in the conventional manufacturing of a filter assembly, it is manufactured in a rolled-up type or a laminated type so that the metallic foam is deformed and lost during the laminating or rolling-up process, thereby degrading the assembling property of the filter assembly.
Conventionally, an adhesive has been used to connect the metallic foams. However, when an adhesive is employed, it should be removed by heating up to about 600° C. for the function of the foam. When heating to such a high temperature, a high-speed heating is required not to damage the metallic foam, but it is not possible by conventional techniques. Therefore, the longer processing time is required. The highly heated adhesive is not completely burned out and partly left as ashes, which may block holes in the metallic form, thereby degrading the function of the metallic foam. Furthermore, when the metallic foam is rolled up after connecting using an adhesive, the connection of metallic foams may be destroyed during the rolling-up process, due to the high tensile strength of the connection portions.